Method for the separation and recovery of krypton and xenon from gaseous mixtures containing them



May 12, 1936. w. WILKINSON ET AL METHOD FOR THE SEPARATION AND RECOVERY OF KRYPTON AND XENON FROM GASEOUS MIXTURES CONTAINING THEM Filed June 11, 1955 2 Sheets-Sheet 1 hm EM ATTORNEYS.

Filed June 11, 1955 2 Sheets-Sheet 2 www INVENTOR ww APE m 5 l f n M ZA wa Q .May 12, 1936.

AND XENON FROM GASEOUS MIXTURES CONTAINING THEM W. WILKINSON ET AL METHOD FOR THE'SEPARATION AND RECOVERY OF KRYP'ION Patented May 12, 1936 PATENT OFFICE METHOD FOR THE SEPARATION AND BE- COVERY OF KRYPTON AND XENON FROM GASEOUS IVII XTURES CONTAINING THEM Walter Wilkinson, Rye, N. Y., and Joseph L.

Schlitt, Darien, Conn., assignors to Air Reduction Company, Incorporated, New York, N. Y., a corporation of New York Application June 11, 1935, Serial No. 26,000

, 5 Claims. This invention relates to a process for separating the rare gases krypton and xenon from gaseous mixtures containing them such as, for example, atmospheric air or the residual by-product of air resulting from the separation of oxygen or nitrogen or both from atmospheric air.

The method forming the subject matter of the present application has for its object the economical production of krypton and. xenon from gaseous mixtures containing them and does not attempt to separate oxygen or nitrogen in purities commercial at the present time.

This method is characterized by the important feature that of the entering gaseous mixture containing krypton and xenon, only a small fraction the gaseous or liquid state and is again separated into'two portions, first a liquid portion carrying substantially all of the krypton-xenon of the original mixture and a residual uncondensed vapor portion, the latter as before being rejected after its cold is recoveredby means of suitable exchangers.

This second condensation portion is again only a small fraction (0.1-0.2) of the total treated fluid resulting from the first condensation and the uncondensed portion is again rejected while the liquid portion either before or after vaporization is still further treated in a relatively small apparatus which completes the separation, that is, which gives as its product a residual uncondensed portion consisting of oxygen and nitrogen impurities and a lower or liquid product constituting the krypton-xenon product of the method.

As a result of the fact that practically all vapors liquefied in this method have compositions not greatly difierent from that of the liquiid which condenses them, it follows that the pressure necessary in any of the fluids that are condensed in order to condense them is very much less than the pressure required in prior air separation methods, for example, where air must be condensed till the uncondensed vapor residue has a composition approximating that of pure nitrogen, by thermal contact with a body of liquid (Cl. Gib-175.5)

oxygen the latter under one atmosphere pressure. The low pressure necessary in the present method ,for producing these necessary condensa tions, results in a further economy in power required, inasmuch as all compressions maybe accomplished by means of machines of the turbo type. Furthermore, this low pressure throughout the system allows the exchange of heat between cold and warm fluids in the exchanger system to be more reversible from a thermodynamic standpoint and thus the efliciency of the whole system isvery materially increased.

Further objects and advantages of the invention will be better understood by reference to the accompanying diagrammatic drawings which illustrate types of apparatus suitable for the practice of the invention. In the drawings,

Fig. 1 shows a practicable apparatus; and

Fig. 2 illustrates a slightly modified arrangement.

The method, as conducted in apparatus shown in Fig. 1, employs for the first two concentrations described above, a method of rectification wherein a reflux liquid obtained from an external source is delivered to the top of a column of rectification trays and meets therein the vapor ascending from below, the liquid as it descends becoming concentrated in krypton and xenon while the vapor as it ascends becomes impoverished in these two constituents. Referring to Fig. l, the entering mixture enters the system through pipe 5 and is compressed to a required pressure in compressor 6 whence the major portion passes through a pipe I and through a compartment 8 of an exchanger 9 wherein it is cooled by outgoing products. From exchanger 9 it passes through pipe Ill to exchanger-H traversing the compartment l2 and leaving the exchanger l-l through pipe 13 by means of which it enters the first rectifier concentrator M;

The vapor ascends the rectifier l4 and contacts directly with liquid descending therein derived from an external source, as hereinafter described, and delivered to the 'top level of rectifier I. As the result of this counter-current contact between liquid and vapor, the krypton-xenon of the entering mixture is all concentrated in the liquid collectingat the bottom l5 of rectifier I I; while the residual vapor, leaving the top of rectifier I 4 and practically freed from krypton and xenon, passes outward through pipe l6 and enters compartment ll of exchanger H. The residual vapor passes thence through pipe Hi to the turboexpander IS, the exhaust of which is divided into two parts.

The main portion passing through pipe 28 enters compartment 2!! of exchanger ii, while the minor portion passing through pipe 22 enters compartment 23 of exchanger 24 and thence through pipe 25 to join the other portion of the exhaust in pipe 26 which delivers the total to compartment 2'! of exchanger 9. Thence it passes outward to the atmosphere,. it may be, through vacuum pump 28.

The second portion of the incoming mixture leaving compressor 6 is conducted through a pipe 29 to the booster compressor 38. Thence the major portion passes through pipe 3! to compartment 32 of exchanger 33 wherein it is cooled down by thermal contact with a suitable outgoing product as hereinafter described. From exchanger 33 it passes through pipe 8% to the coil 35 located at the bottom of the evaporatorrectifier 96 wherein it is liquefied and passes thence through pipe 3? and pressure reducing valve 38 to the top level of rectifier M consituting the top liquid reflux for that rectifier.

The liquid product of rectifier M collecting at the bottom i5 leaves the liquid pool through pipe 39 and enters the bottom of the rectifier-evaporator 36, wherein its equivalent is evaporated from the liquid pool at the bottom of rectifier 36 as above described. The vapor from this evaporation passing upward in rectifier 36 comes in contact with a liquid reflux delivered to the top level ll] of that rectifier and the vapor product leaves rectifier 36 through pipe ll entering compartment Q2 of exchanger 33 and thence passes to the outside where it is rejected.

The lower liquid product of evaporator-rectifier 36 leaves the bottom through pipe 53 and enters anintermediate level of the double rectifier d9 wherein it cascades over trays and collects in a liquid pool at the bottom. A portion of the air leaving booster compressor 30 is diverted through pipe G5 to the small booster compressor 86 wherein it is compressed to a pressure suitable for condensation in a coil at the bottom of rectifier M. This triple compressed air leaves compressor t6 through a pipe 61 and enters compartment d8 of the exchanger 39 and thence through compartment 58 of exchanger 2% and thence through a pipe 5i through evaporating coil 52 at the bottom of rectifier d4. After being liquefied by thermal contact with the liquid collecting at the bottom of rectifier i l, it is conducted through a pipe 53 and pressure reducing valve 53 to serve as top reflux for both rectifiers 39 and 44, that portion passing to rectifier M traversingvalve 55 whereas that portion which refiuxes' rectifier 36 passes through valve 40'.

The upper uncondensed product of rectifier 38, substantially free from krypton and xenon, passes outward through pipe 56 to compartment 51 of exchanger 49 and is then rejected. The-lower end or krypton-xenon product of rectifier M is v abstracted in either the liquid or in the vapor of the vapor to be condensed and the liquid by state or both by means of valves 58 and 59 respectively, joining together in pipe 68 and then entering compartment fil'of exchanger 49 where its temperature is reduced to that of the surrounding atmosphere.

From the foregoing description, it is clear that means of which it is condensed are not greatly different, the pressure requirement for all condensations is relatively very small and easily within the pressure range for machines of the turbo type. Furthermore, by the judicious use of a turbo-vacuum compressor 28 the expansion ratio of turbo-expander 89 may be easily and eificiently made sufficient for all refrigeration needs of the system. Rectifier M in which the final separation is completed is a very small piece of apparatus relative to rectifier 38 which in turn is very small relative to the first rectifier it.

Fig. 2 illustrates an alternative arrangement of apparatus in which the first two krypton-xenon concentrations are accomplished by means of successive condensations out of a portion of the incoming mixture. In this alternative arrangement, the minor fraction (0.1) of the original mixture which is condensed is evaporated after its pressure has been lowered bypressure reducing valves, by acting as a condensing fluid in the first concentration. It is then restored to atmospheric temperature and again compressed, after which it passes through suitable exchangers and enters in the vapor state the second concentrator or rectifier, and in turn is divided into two portions, (1) a lower liquid portion and (2) an upper uncondensed vapor portion. The liquid portion, that is, the krypton-xenon concentrate from this second concentrator after passing. a pressure reducing valve, acts as condensing fluid at the top of the second concentrator in a manner precisely similar to that employed by the liquid obtained at the bottom of the first concentrator. After being evaporated in this manner, its temperature is restored to atmospheric and its pressure is again raised by a small compressor after which; passing through a suitable exchanger, it enters an intermediate level of the final rectifier wherein it is separated into an upper end vapor product consisting of oxygen and nitrogen and a lower liquid product constituting the krypton-xenon product.

Referring to Fig. 2 of the drawings, the gaseous mixture is introduced through a, pipe 52 and is compressed to the desired pressure in a suitable compressor or blower (53. It passes thence through a pipe 9 to a compartment 65 of the exchanger 66 and thence through a pipe 5i to a compartment 58 of the changer 89. A pipe it delivers the incoming gaseous mixture to the rectifier Ill, wherein it passes upwardly through the usual trays l2 and is partially liquefied by contact with the liquid flowing downwardly produced at the upper end of the rectifier by contact with the coil l3. To this coil the liquid concentrate from the bottom of the rectifier is delivered through a pipe M and expansionvalve B5. The unliquefied residue or effluent escapes through a pipe 16, passes through a compartment ll of the exchanger 89 and thence through a pipe 78 to the turbo-expander i9. A pipe 80 delivers the efiiuent cooled by expansion to the chamber 8! of the exchanger 69. Thence it passes through a pipe 82 to the chamber 83 of the exchanger 56 and escapes through a pipe 84.

The vapor from the coil 13 is delivered through a pipe 85 to a chamber 86 of the exchanger 56 and passes through a, pipe 81 to a booster-compressor 88, preferably of the turbo type. The vapor is delivered through a pipe 89 to a compartment 90 of an exchanger 9|, and thence through a pipe 92 to the bottom of a rectifier 93. The vapor passes up through the usual trays 94 and is partially liquefied by contact with a coil r to the top. of the column'through dis ment 99 of the exchanger 9|, and thence through the outlet pipe I00.

The vapor formed in the coil 95 is delivered through the'pipe IM to the chamber I02 the exchanger 9|, and .thence through a pipe I02 to a booster-compressor, I04 preferably of the turbo type. After compression, ,the vapor passes through the pipe I05 to a chamber I06 of an exchanger I01 and thence through a pipe I08 to an intermediate levelof a rectifier I09. The-vapor rises through the usual trays H0 jected to the washing action of a liquid delivered a pipe III. consisting of nitrogen,

II2 to a compart- I0'|, v and thence The emuent, oxygen, escapes through a pipe ment lll of the exchanger through theoutlet pipe II4. V

The liquid supplied through the pipe I I I results from liquefaction of a portion of the incoming mixture delivered by a, booster-compressor II5,

the turbo type, through a pipe IIG preferably of of the exchanger I01 and compartment II'I whence itpasses through a pipe I I8 to a coil I I9 in the bottom of the rectifier I09. The liquidiormed in the coil is delivered through a pipe I20 and pressure reducing valve I2I to the n i? 7 In liquefying the gaseous mixture in the coil 9, the krypton-xenon concentrate which collects as' a liquid in the bottom ofthe rectifier I09 is vaporized, ajportion of the vapor passing upwardly and being recondensed in the rectifier; The liquid is withdrawn through a pipe I22 and pressure reducing valve I23,- and it is joined by a portion of the vapor withdrawn through the pressure reducing valve I24; A pipe I25 delivers the krypton-xenon concentrate to a compartment I26 of the exchanger I01, whence it escapes through the outlet pipe I21 as the product of the separation.

To assist in cooling the exchangers 9I and I01, a portion ofthe expanded eiiiuentm'a-y be diverted from the pipe 80 through a pipe I28- A pipe I29, including valve 130, delivers the efiluent to the compartment I3I of the exchanger 9|. Similarly a pipe I32 provided with a valve I33 delivers a portionof the diluent to the compartment I34 of delivers the eiiiuent to 'a pipe I36 connected to the compartment I3I which is connected to the compartment. ofthe exchanger 00.

The procedure as described is substantially that described inconnection with respect to the utilization of the liquid collected at the bottom of each of the first two rectifiers as a cooling agent, to liquefy vapors at the top of each of the respective rectifiers. As in the preceding embodiment of the invention, the desired result is accomplished by successive concentrations with other than krypton and xenon constituting the product of the operation.

subjecting a and is subrejecting in krypton and xenon.

the exchanger I0'I. A pipe I35 treated to Fig. 1 except inpor irom the the elimination of constituentsv Various changes may be made in the form and arrangement of the apparatus as well as in the procedure outlined without departing from the invention or sacrificing any of 1. The method of separating krypton and xenon from air which {comprises portion of the incoming air to liqueiaction and rectification in a plurality of steps, rejecting in each step the unliquefied portion of the air treated and producing thereby a concentrate rich in krypton and xenon, and finally rectifying the concentrate with a further portion of the air, thereby enriching th concentratein krypton and xenon. 2. The method of krypton and xenon from subjecting a portion-oi! the uefaction and rectification in aplurality of steps,

each

:eiiiuent from the final rectification- 3. The method of separating and, recovering krypton and xenon from air which comprises subjecting a portion of the air to liquefaction and rectification to produce a and xenon, vaporizing the liquid rich in krypton liquid product and subjecting it' to a second liquefaction and rectification, rejecting in each step the upper eilluent from the rectification and producing thereby a concentrate rich in krypton and xenon and final 1y. rectifying the concentrate with a further portion of air, thereby enriching the concentrate in 4. The method of separating and recovering krypton and xenon rom air which comprises subjectinga portion of the air to liquefaction and rectification .to

and xenon, vaporizing the liquid product and subjecting it to a second liquefaction and rectification and producing thereby a concentrate rich in krypton and xenon and finally rectifying the concentrate with a further portion of air, thereby enriching the concentrate-in krypton" and xenon, and rejecting the eiilue t from the final rectification.

5. The method of separating and recovering, krypton-and xenon from airwhich. comprises liqueiying selectively secure a. liquid enriched in krypton and xenon, evaporating the liquidto. efiect by heat exchange the selective liquefaction of the incoming air, recompressing and cooling the vaenriched liquid, subjecting the partial liquefaction, rectifying vapor to further the liquid products with oi! the rectification consisting essentially of krypton and xenon.

WALTER- SON. JOSE H L.

the advantages step the unliquefied portion of. the air treated and producing thereby a conproduce a'liquid rich in krypton the addition of a relatively large volume of unseparated air, and with-' drawing thev liquid product and recovering a portion 0! the air to be 

